Oh, you are aussie:) i should have guessed by your username.

Ok, for starters, where I live that big yellow thing stops shining. Practically (for electricity production anyways) for almost 6 months of the year and almost totally for 3. And even with heat pumps we still use several MWh of electricity every year to heat our homes. A battery park can keep a city running for 1h. Even those planned in NSW (BESS is it?) would struggle to keep things running for mire than a day. To be clear:

We need more energy storage than can be provided by electric batteries, than can be bought at battery prices and in scales larger than can be produced with any technology current or in the overseeable future. And we needed it yesterday. Any form of low cost, stable, easy to store solution we can use is a huge step forward. Solar is great! But we need the electricity when the sun doesn’t shine. Heat pumps are awesome! But their awesomness is needed when the sun doesn’t shine so much. That is why we need more energy storage solutions.

Summertime there are almost limitless electricity available, but that energy needs to be stored somehow. And with limitless (in practice) efficiency isn’t an issue. Even storing 1% is better than 0%. Regardless of efficiency.